1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * https://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17
18 /*
19 * This is not the original file distributed by the Apache Software Foundation
20 * It has been modified by the Hipparchus project
21 */
22
23 package org.hipparchus.ode.nonstiff;
24
25 import org.hipparchus.CalculusFieldElement;
26 import org.hipparchus.Field;
27 import org.hipparchus.ode.FieldEquationsMapper;
28 import org.hipparchus.ode.FieldODEStateAndDerivative;
29 import org.hipparchus.ode.nonstiff.interpolators.ClassicalRungeKuttaFieldStateInterpolator;
30 import org.hipparchus.util.MathArrays;
31
32 /**
33 * This class implements the classical fourth order Runge-Kutta
34 * integrator for Ordinary Differential Equations (it is the most
35 * often used Runge-Kutta method).
36 *
37 * <p>This method is an explicit Runge-Kutta method, its Butcher-array
38 * is the following one :</p>
39 * <pre>
40 * 0 | 0 0 0 0
41 * 1/2 | 1/2 0 0 0
42 * 1/2 | 0 1/2 0 0
43 * 1 | 0 0 1 0
44 * |--------------------
45 * | 1/6 1/3 1/3 1/6
46 * </pre>
47 *
48 * @see EulerFieldIntegrator
49 * @see GillFieldIntegrator
50 * @see MidpointFieldIntegrator
51 * @see ThreeEighthesFieldIntegrator
52 * @see LutherFieldIntegrator
53 * @param <T> the type of the field elements
54 */
55
56 public class ClassicalRungeKuttaFieldIntegrator<T extends CalculusFieldElement<T>>
57 extends FixedStepRungeKuttaFieldIntegrator<T> {
58
59 /** Name of integration scheme. */
60 public static final String METHOD_NAME = ClassicalRungeKuttaIntegrator.METHOD_NAME;
61
62 /** Simple constructor.
63 * Build a fourth-order Runge-Kutta integrator with the given step.
64 * @param field field to which the time and state vector elements belong
65 * @param step integration step
66 */
67 public ClassicalRungeKuttaFieldIntegrator(final Field<T> field, final T step) {
68 super(field, METHOD_NAME, step);
69 }
70
71 /** {@inheritDoc} */
72 @Override
73 public T[] getC() {
74 final T[] c = MathArrays.buildArray(getField(), 3);
75 c[0] = getField().getOne().newInstance(0.5);
76 c[1] = c[0];
77 c[2] = getField().getOne();
78 return c;
79 }
80
81 /** {@inheritDoc} */
82 @Override
83 public T[][] getA() {
84 final T[][] a = MathArrays.buildArray(getField(), 3, -1);
85 for (int i = 0; i < a.length; ++i) {
86 a[i] = MathArrays.buildArray(getField(), i + 1);
87 }
88 a[0][0] = FieldExplicitRungeKuttaIntegrator.fraction(getField(), 1, 2);
89 a[1][0] = getField().getZero();
90 a[1][1] = a[0][0];
91 a[2][0] = getField().getZero();
92 a[2][1] = getField().getZero();
93 a[2][2] = getField().getOne();
94 return a;
95 }
96
97 /** {@inheritDoc} */
98 @Override
99 public T[] getB() {
100 final T[] b = MathArrays.buildArray(getField(), 4);
101 b[0] = FieldExplicitRungeKuttaIntegrator.fraction(getField(), 1, 6);
102 b[1] = FieldExplicitRungeKuttaIntegrator.fraction(getField(), 1, 3);
103 b[2] = b[1];
104 b[3] = b[0];
105 return b;
106 }
107
108 /** {@inheritDoc} */
109 @Override
110 protected ClassicalRungeKuttaFieldStateInterpolator<T>
111 createInterpolator(final boolean forward, T[][] yDotK,
112 final FieldODEStateAndDerivative<T> globalPreviousState,
113 final FieldODEStateAndDerivative<T> globalCurrentState,
114 final FieldEquationsMapper<T> mapper) {
115 return new ClassicalRungeKuttaFieldStateInterpolator<>(getField(), forward, yDotK,
116 globalPreviousState, globalCurrentState,
117 globalPreviousState, globalCurrentState,
118 mapper);
119 }
120
121 }